1. Field of the Invention
The present invention relates to a liquid ejection head and an ejection abnormality determination method, more particularly to ejection abnormality determination technology which determines abnormalities in a plurality of ejection apertures which do not perform ejection during an ejection operation in an ejection head having the plurality of ejection apertures.
2. Description of the Related Art
In recent years, inkjet recording apparatuses have come to be used widely as data output apparatuses for outputting images, documents, or the like. By driving recording elements, such as nozzles, provided in a recording head in accordance with data, an inkjet recording apparatus is able to form data onto a print medium (recording medium), such as recording paper, by means of ink ejected from the nozzles.
In an inkjet recording apparatus, a desired image is formed on a print medium by causing a print head having a plurality of nozzles and a print medium to move relatively to each other, while causing ink droplets to be ejected from the nozzles.
In an inkjet recording apparatus, when the ink inside the nozzles makes contact with the air, the ink solvent evaporates from the surface of the ink in contact with the air and the viscosity of the ink increases. If ink whose viscosity has increased in this manner is used, nozzle blockages become liable to occur and this may lead to ejection failures or ejection abnormalities.
Furthermore, if air bubbles become mixed into the pressure chambers of the recording head, then there is significant loss of the pressure applied to the ink by the actuators, and this can lead to ejection abnormalities, such as abnormalities in the amount of ink ejected or the direction of ejection, ejection failures, and the like.
If ejection abnormalities occur as described above, then the image quality deteriorates markedly, and therefore, it is possible to maintain the quality of the recorded image by determining ejection abnormalities of this kind promptly, and eliminating the causes of the ejection abnormalities. In ejection abnormality determination according to the related art, a method is proposed in which the characteristics of a piezoelectric element, or the waveform during driving of a piezoelectric element, is measured and the presence of air bubbles in the pressure chamber (ink chamber) or the presence of an ejection abnormality in a nozzle is determined accordingly.
The need for air bubble determination or ejection abnormality determination of this kind becomes more important in the case of a print head having a multiple-nozzle structure.
On the other hand, in a multiple-nozzle structure, and in particular, a line head, which is the ultimate mode of a multiple-nozzle structure, since the number of nozzles is very large, there may be nozzles which do not perform ejection for a relatively long period of time, depending on the print data. Nozzles of this kind are liable to enter a state which leads to ejection abnormalities, and therefore technology has been proposed which churns the ink in the vicinity of the nozzles by applying a vibration to the ink to a degree that not does cause ejection of the ink, thereby preventing increase in the viscosity of the ink.
More specifically, in a method for suppressing increase in the viscosity of the ink in the nozzles by vibrating the meniscus surface of the ink by means of the actuators used for ink ejection, it is possible to apply a low voltage or a high-frequency voltage to the actuators at a level which does not cause ejection of ink from the nozzles, thereby churning the ink in the vicinity of the meniscus surface and slowing the increase in the viscosity of the ink.
Japanese Patent Application Publication No. 60-262655 discloses an ink ejection device, in which electrical distortion elements are provided as means of changing the internal pressure of the ink inside ink chambers of an on-demand type inkjet head, and a drive circuit for driving the head is provided, in addition to a vibration analyzing and determining device which determines the intrinsic vibration of the head caused by the potential difference generated between the electrodes of the electrical distortion element, simultaneously with the driving of the head. A device is provided for expelling air bubbles from inside the ink flow channels when air bubbles are determined to be present in the ink flow channels by this determining device.
Japanese Patent Application Publication No. 2000-318183 discloses a replenishment determination apparatus and replenishment determination method for the recording head of a printer, in which the state of replenishment of the ink in the recording head is determined electrically by obtaining the profile of the resonance point of piezoelectric elements applying an ejection pressure to ink.
Japanese Patent Application Publication No. 2000-355100 discloses a printer apparatus, in which nozzle determination method and print method described in, piezoelectric elements provided respectively at nozzles are driven by applying a measurement input signal to the piezoelectric elements, a phase output waveform representing the phase divergence between the measurement input voltage and the measurement output voltage after driving the piezoelectric elements is generated, together with a peak output waveform representing the amplitude of the measurement output waveform, and the nozzles are inspected by comparing these waveforms with the frequency characteristics of a previously prepared phase output waveform and peak output waveform.
Japanese Patent Application Publication No. 11-334102 discloses air bubble determination circuit and air bubble determination method in an inkjet printer, in which the impedance of the piezoelectric elements of the head is measured at an arbitrary frequency, the frequency characteristics of the impedance are compiled, and it is determined whether or not air bubbles are attached to the piezoelectric elements on the basis of these frequency characteristics.
Japanese Patent Application Publication No. 11-309874 discloses an inspection method for a liquid ejection apparatus, in which an excitation element and a reflection plate are disposed facing each other on either side of the line linking a vibrating body and a nozzle plate, and when the excitation element applies a vibration directly to the ink inside the ink chamber, then this vibration is reflected by the reflection plate and returned again to the excitation element, this returning vibration being acquired as a determination signal and being analyzed by means of an excitation/determination device.
However, in the ejection abnormality determination according to the related art, a plurality of determination operations are required in order to judge the respective nozzles, and in the case of a head having a large number of nozzles, in particular, the time required for the whole determination operation becomes large, and this ultimately reduces the high print capacity (productivity) originally achieved by adopting a large number of nozzles in the head.
Furthermore, in the ejection abnormality determination according to the related art, in a method which determines abnormalities by actually ejecting ink or a method which determines abnormalities without actually ejecting ink, ultimately, ink is ejected and the determination operation cannot be performed during printing.
In the ink ejection apparatus described in Japanese Patent Application Publication No. 60-262655, it is difficult to set the threshold value for judging ejection abnormalities, since the potential difference generated between the electrodes of the electrical distortion elements is a very low voltage. Furthermore, since analogue values are measured and analyzed, the S/N ratio is low and therefore it is essential that judgment is made on the basis of a plurality of measurements (determination operations) and statistical processing, or the like.
Furthermore, in the replenishment determination apparatus and replenishment determination method for the recording head of a printer as described in Japanese Patent Application Publication No. 2000-318183, the printer apparatus, nozzle determination method and print method described in Japanese Patent Application Publication No. 2000-355100, the inkjet printer, air bubble determination circuit and air bubble determination method described in Japanese Patent Application Publication No. 11-334102, and the determination method for a liquid ejection apparatus described in Japanese Patent Application Publication No. 11-309874, it is necessary perform determination over a broad frequency range, from a low-frequency region to a high-frequency region. Furthermore, the analogue signal handled in this case has a low S/N ratio and therefore it is essential that judgment is made on the basis of a plurality of measurements (determination operations) and statistical processing, or the like.